Help text

SD/MMC is a high latency protocol where it is crucial to
send large requests in order to get high performance. Many
controllers, however, are restricted to continuous memory
(i.e. they can't do scatter-gather), something the kernel
rarely can provide.

Say Y here to help these restricted hosts by bouncing
requests back and forth from a large buffer. You will get
a big performance gain at the cost of up to 64 KiB of
physical memory.